minor #22948 [Yaml] Recommend using quotes instead of PARSE_KEYS_AS_STRINGS (GuilhemN)
minor #22948 [Yaml] Recommend using quotes instead of PARSE_KEYS_AS_STRINGS (GuilhemN)

This PR was squashed before being merged into the 3.4 branch (closes #22948).

Discussion
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[Yaml] Recommend using quotes instead of PARSE_KEYS_AS_STRINGS

| Q             | A
| ------------- | ---
| Branch?       | 3.4
| Bug fix?      | no
| New feature?  | no <!-- don't forget updating src/**/CHANGELOG.md files -->
| BC breaks?    | no
| Deprecations? | yes <!-- don't forget updating UPGRADE-*.md files -->
| Tests pass?   | yes
| Fixed tickets | #... <!-- #-prefixed issue number(s), if any -->
| License       | MIT
| Doc PR        |

Sorry for opening this so lately... I just realized that we could get rid of `Yaml::PARSE_KEYS_AS_STRINGS` just by recommending using quotes...

~This way we don't allow a behavior not respecting the spec and we won't need to deprecate `PARSE_KEYS_AS_STRINGS` later.~

~Is it too late for this to be merged in 3.3?~

ping @xabbuh

Commits
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b63c55c [Yaml] Recommend using quotes instead of PARSE_KEYS_AS_STRINGS

symfony/DependencyInjection,symfony/dependency-injection